In recent years, an observation camera is installed in a store, a busy street or a condominium and a drive recorder is installed in a business use vehicle as usual, and moving image data is treated as evidence in an increasing number of cases. Further, it is in the process of being a common sense that a store records a conversation between a customer and an operator and keeps the record as evidence in order to deal with a trouble concerning trading on the phone or supporting business.
The store provides a videotape or an image or audio file as it is at present so as to give moving image data or voice as evidence. If, however, image or voice is stored increasingly in digital forms, it can be easily altered or edited and thus will ask for third-party authentication such as a signature or timestamp so as to be treated as evidence. Services or products which record voice of a telephone operator with a timestamp are on sale in practice. It is expected that these kinds of technologies will be increasingly in demand.
Incidentally, a method for dividing contents in an electronic document into headings, calculating summary data of each of the headings, and adding an electronic signature to collection of the summary data of each of the headings is used as a technology for detecting a third-party's alteration. The summary data mentioned here corresponds to hash data calculated by the use of a cryptographic one-way hash function called a message digest.
Further, a technology for providing an image file with an expanded area and recording related data together with image data is disclosed with regard to image filing. Further, another technology for providing an image file with an expanded area and recording a plurality of copies or partial copies of appended data corresponding to image data is disclosed with regard to image filing (Japanese Laid-open Patent Publications No. 2005-33503 and No. 2004-5934, e.g., discuss those technologies).
Further, a form of Internet service called cloud computing (called “cloud” hereafter) in which a user can use services provided by servers on the network without being aware of them has been mainstreamed in recent years. Services for using the cloud so as to pile up and manage digitized moving images and voices in a center server in the cloud and to distribute content are being mainstreamed.